With the increasing performance of processors and switching chips, a similar increase in bandwidth requirements for incoming and outgoing data also exists. In certain cases, electrical interconnects can provide bandwidth limitations for microelectronic chips. These limitations are a result of maximum electrical line density and maximum data rates per line. One potential solution to this higher bandwidth requirement is the use of optical components and optical communication connections. Simply stated, optical communications is capable of operating at higher speeds per line, and a higher line density. As such, higher bandwidth density is achievable using optical signals.
High density and high speed data is preferably made available at the top of a chip carrier, immediately adjacent to a processor. As such, this is the optimum location to place those components which convert data from electrical to optical signals and vice-versa. As recognized by those skilled in the art, this typically involves the placement of lasers or optical detectors at the top of the chip carrier, immediately adjacent the processor. This placement however creates a complication when attempting to communicate high speed optical signals from the top of the chip carrier to appropriate components in a related circuit board. For example, the printed circuit board may include embedded waveguides, or fiber optic interconnects which carry the optical signals to related components.
To achieve transmission of optical signals from the optoelectronic component to appropriate signal carrying structures, existing chip carriers typically include a window or lens on a bottom surface thereof. This lens or window is obviously aligned with the optoelectronic component, thus allowing optical signals to be transmitted from (or received at) the bottom side of the chip carrier. In this particular approach, two design complications exist: (1) the distance the optical signals must travel, and (2) appropriate alignment of the window with related optical structures. The distance to the circuit board creates issues due to the potential divergence of the optical signal, which leads to a limited signal strength and crosstalk between signals. Typical optoelectronic structures as applied in datacom applications are capable of transmitting signals approximately two millimeters or so while also achieving appropriate transmission performance. Naturally, the power level and signal strength may have some bearing on this distance. As also mentioned, alignment is an issue. Typical printed circuit boards do not require tight dimensional tolerances, thus the exact placement of components can vary somewhat. Unfortunately, the alignment of optical components necessarily requires tighter tolerances and more precision. Thus, the differences in these tolerances alone can cause misalignment.
In light of the above issues, a better approach to optical signal transfer is necessary for use in optoelectronic circuit assemblies. Such an approach will appropriately bridge the gap that will exist between optoelectronic components and signal carrying structures embedded within a printed circuit board.